This invention relates to methods of forming non-volatile resistance variable devices and to sputtering methods of forming a metal layer comprising silver and tungsten.
Semiconductor fabrication continues to strive to make individual electronic components smaller and smaller resulting in ever denser integrated circuitry. One type of integrated circuitry comprises memory circuitry where information is stored in the form of binary data. The circuitry can be fabricated such that the data is volatile or non-volatile. Volatile storing memory devices result in loss of data when power is interrupted. Non-volatile memory circuitry retains the stored data even when power is interrupted.
This invention was principally motivated in making improvements to the design and operation of memory circuitry disclosed in U.S. Pat. Nos. 5,761,115; 5,896,312; 5,914,893; and 6,084,796 to Kozicki et al., which ultimately resulted from U.S. patent application Ser. No. 08/652,706, filed on May 30, 1996, now U.S. Pat. No. 5,761,115 disclosing what is referred to as a programmable metallization cell. Such a cell includes opposing electrodes having an insulating dielectric material received therebetween. Received within the dielectric material is a variable resistance material. The resistance of such material can be changed between low resistance and high resistance states. In its normal high resistance state, to perform a write operation, a voltage potential is applied to a certain one of the electrodes with the other of the electrode being held at zero voltage or ground. The electrode having the voltage applied thereto functions as an anode, while the electrode held at zero or ground functions as a cathode. The nature of the resistance variable material is such that it undergoes a change at a certain applied voltage. With such voltage applied, a low resistance state is induced into the material such that electrical conduction can occur between the top and bottom electrodes.
Once this occurs, the low resistance state is retained when the voltage potentials are removed. Such can effectively result in the resistance of the mass of resistance variable material between the electrodes dropping by a factor of 1,000. Such material can be returned to its highly resistive state by reversing the voltage potential between the anode and cathode. Again, the highly resistive state is maintained once the reverse voltage potentials are removed. Accordingly, such a device can, for example, function as a programmable memory cell of memory circuitry.
The preferred resistance variable material received between the electrodes typically and preferably comprises a chalcogenide material having metal ions diffused therein. One specific example includes one or more layers of germanium selenide having silver ions diffused therein and one or more layers of silver selenide having excess silver ions diffused therein. Typically in such example, one or both of the electrodes will comprise silver, for example elemental silver. One promising electrode material for such cells is a mixture or alloy of silver and tungsten. A primary motivation in this invention relates to improving sputtering techniques in forming at least one of the electrodes to comprise a metal layer comprising silver and tungsten.
The invention includes methods of forming a non-volatile resistance variable device and methods of forming a metal layer comprising silver and tungsten. In one implementation, a method of forming a non-volatile resistance variable device includes forming a chalcogenide material over a semiconductor substrate. First and second electrodes are formed operably proximate the chalcogenide material. At least one of the first and second electrodes includes a metal layer comprising silver and tungsten. The metal layer is formed by providing the substrate within a sputter deposition chamber. One or more target(s) is/are provided within the chamber which include(s) at least tungsten and silver. The one or more target(s) is/are sputtered using a sputtering gas comprising at least one of Xe, Kr and Rn under conditions effective to deposit the metal layer onto the substrate. The invention contemplates fabrication of the metal layer independent of fabrication of a non-volatile resistance variable device.